Washing units comprising one or more washing tanks through which the photographic material successively passes are known for the treatment of photographic material in a continuous transport system. The fresh water normally required for this purpose is introduced into the last of the washing tanks so that the concentration of treatment chemicals to be dissolved out from the photographic layer is lowest in that tank. The overflow from the last washing tank is then guided into the preceding washing tanks so that the concentration of chemicals increases against the direction of movement of the photographic material. This principle is known as the countercurrent principle both from the standpoint of chemical process engineering and from the standpoint of heat exchangers. The treatment results obtained are better, the greater the number of consecutive treatment steps. However, the expense involved in a treatment system such as this increases with the number of tanks.
A system of the type in question is known, for example, from DE-C-33 20 787, its effect being enhanced by the arrangement of an overflow weir with drainage channel, which extends over the entire width of the tank, on the entry side of, and beneath, the photographic material and by the provision of a first pair of rollers extending over the width of the tank, of which the axial plane is inclined towards the water level, a narrow gap in relation to the length of the tank remaining between the drainage channel and the adjacent roller of the pair of rollers; a water spray pipe parallel to the rollers with outlet openings directed substantially upwards is arranged in the lower part of the tank, extending over the width thereof, in such a way that the jet issuing from the spray pipe is directed onto the gap between the drainage channel and the roller.
This system may also be used in a no-wash processing cycle in which the final wash is replaced by treatment of the material with a stabilizing solution. However, the increase in effectiveness over systems without a spray pipe is not so great that the number of tanks for the stabilizer treatment could be reduced.
In a no-wash processing cycle with stabilizer treatment as the final bath, four tanks for the treatment with stabilizing solution are normally arranged in the form of a countercurrent cascade and are operated with a regeneration quota of 248 ml/m.sup.2 and a residence time of 22.5 secs./tank, a carryover rate of approx. 80 ml/m.sup.2 having to be taken into account.
At present, it is known that the following measures have to be taken to reduce the number of tanks to only three for the same throughput of material and the same desired dilution effect: increasing the regeneration quota to at least 400 ml/m.sup.2, which is counterproductive because it leads to a considerable increase in the accumulation of spent stabilizing bath.